%  -----------------------------------------------------------------------------
%
%                            procedure dpper
%
%   this procedure provides deep space long period periodic contributions
%     to the mean elements.  by design, these periodics are zero at epoch.
%     this used to be dscom which included initialization, but it's really a
%     recurring function.
%
% Author: 
%   Jeff Beck 
%   beckja@alumni.lehigh.edu
%   1.0 (aug 7, 2006) - update for paper dav
% original comments from Vallado C++ version:
%   author        : david vallado                  719-573-2600   28 jun 2005
%
%   inputs        :
%     e3          -
%     ee2         -
%     peo         -
%     pgho        -
%     pho         -
%     pinco       -
%     plo         -
%     se2 , se3 , Sgh2, Sgh3, Sgh4, Sh2, Sh3, Si2, Si3, Sl2, Sl3, Sl4 -
%     t           -
%     xh2, xh3, xi2, xi3, xl2, xl3, xl4 -
%     zmol        -
%     zmos        -
%     ep          - eccentricity                           0.0 - 1.0
%     inclo       - inclination - needed for lyddane modification
%     nodep       - right ascension of ascending node
%     argpp       - argument of perigee
%     mp          - mean anomaly
%
%   outputs       :
%     ep          - eccentricity                           0.0 - 1.0
%     inclp       - inclination
%     nodep       - right ascension of ascending node
%     argpp       - argument of perigee
%     mp          - mean anomaly
%
%   locals        :
%     alfdp       -
%     betdp       -
%     cosip  , sinip  , cosop  , sinop  ,
%     dalf        -
%     dbet        -
%     dls         -
%     f2, f3      -
%     pe          -
%     pgh         -
%     ph          -
%     pinc        -
%     pl          -
%     sel   , ses   , sghl  , sghs  , shl   , shs   , sil   , sinzf , sis   ,
%     sll   , sls
%     xls         -
%     xnoh        -
%     zf          -
%     zm          -
%
%   coupling      :
%     none.
%
%   references    :
%     hoots, roehrich, norad spacetrack report #3 1980
%     hoots, norad spacetrack report #6 1986
%     hoots, schumacher and glover 2004
%     vallado, crawford, hujsak, kelso  2006
%  ----------------------------------------------------------------------------*/

function [  ep,     inclp,  nodep, argpp,  mp]...
          = dpper(...
            e3,     ee2,    peo,    pgho,   pho,    pinco,  plo,    se2,...
            se3,    sgh2,   sgh3,   sgh4,   sh2,    sh3,    si2,    si3,...
            sl2,    sl3,    sl4,    t,      xgh2,   xgh3,   xgh4,   xh2,...
            xh3,    xi2,    xi3,    xl2,    xl3,    xl4,    zmol,...
            zmos,   inclo,  init,   ep,     inclp,  nodep, argpp,  mp, opsmode)

   % change to variable passed in
   % global opsmode

   % /* --------------------- local variables ------------------------ */
   twopi = 2.0 * pi;

   % /* ---------------------- constants ----------------------------- */
   zns   = 1.19459e-5;
   zes   = 0.01675;
   znl   = 1.5835218e-4;
   zel   = 0.05490;

   % /* --------------- calculate time varying periodics ----------- */
   zm    = zmos + zns * t;
   % // be sure that the initial call has time set to zero
   if (init == 'y')
       zm = zmos;
   end
   zf    = zm + 2.0 * zes * sin(zm);
   sinzf = sin(zf);
   f2    =  0.5 * sinzf * sinzf - 0.25;
   f3    = -0.5 * sinzf * cos(zf);
   ses   = se2* f2 + se3 * f3;
   sis   = si2 * f2 + si3 * f3;
   sls   = sl2 * f2 + sl3 * f3 + sl4 * sinzf;
   sghs  = sgh2 * f2 + sgh3 * f3 + sgh4 * sinzf;
   shs   = sh2 * f2 + sh3 * f3;
   zm    = zmol + znl * t;
   if (init == 'y')
       zm = zmol;
   end
   zf    = zm + 2.0 * zel * sin(zm);
   sinzf = sin(zf);
   f2    =  0.5 * sinzf * sinzf - 0.25;
   f3    = -0.5 * sinzf * cos(zf);
   sel   = ee2 * f2 + e3 * f3;
   sil   = xi2 * f2 + xi3 * f3;
   sll   = xl2 * f2 + xl3 * f3 + xl4 * sinzf;
   sghl  = xgh2 * f2 + xgh3 * f3 + xgh4 * sinzf;
   shll  = xh2 * f2 + xh3 * f3;
   pe    = ses + sel;
   pinc  = sis + sil;
   pl    = sls + sll;
   pgh   = sghs + sghl;
   ph    = shs + shll;

   if (init == 'n')
       %   //  0.2 rad = 11.45916 deg
       pe    = pe - peo;
       pinc  = pinc - pinco;
       pl    = pl - plo;
       pgh   = pgh - pgho;
       ph    = ph - pho;
       inclp = inclp + pinc;
       ep    = ep + pe;
       sinip = sin(inclp);
       cosip = cos(inclp);

       % /* ----------------- apply periodics directly ------------ */
       %   //  sgp4fix for lyddane choice
       %   //  strn3 used original inclination - this is technically feasible
       %   //  gsfc used perturbed inclination - also technically feasible
       %   //  probably best to readjust the 0.2 limit value and limit discontinuity
       %   //  use next line for original strn3 approach and original inclination
       %   //  if (inclo >= 0.2)
       %   //  use next line for gsfc version and perturbed inclination
       if (inclp >= 0.2)
           ph     = ph / sinip;
           pgh    = pgh - cosip * ph;
           argpp  = argpp + pgh;
           nodep  = nodep + ph;
           mp     = mp + pl;
       else
           % /* ---- apply periodics with lyddane modification ---- */
           sinop  = sin(nodep);
           cosop  = cos(nodep);
           alfdp  = sinip * sinop;
           betdp  = sinip * cosop;
           dalf   =  ph * cosop + pinc * cosip * sinop;
           dbet   = -ph * sinop + pinc * cosip * cosop;
           alfdp  = alfdp + dalf;
           betdp  = betdp + dbet;
           nodep  = rem(nodep, twopi);
           % sgp4fix for afspc written intrinsic functions 
           % nodep used without a trigonometric function ahead 
           if ((nodep < 0.0) && (opsmode == 'a'))
               nodep = nodep + twopi;
             end
           xls    = mp + argpp + cosip * nodep;
           dls    = pl + pgh - pinc * nodep * sinip;
           xls    = xls + dls;
           xnoh   = nodep;
           nodep  = atan2(alfdp, betdp);
           % sgp4fix for afspc written intrinsic functions 
           % nodep used without a trigonometric function ahead 
           if ((nodep < 0.0) && (opsmode == 'a'))
               nodep = nodep + twopi;
             end
           if (abs(xnoh - nodep) > pi)
               if (nodep < xnoh)
                   nodep = nodep + twopi;
               else
                   nodep = nodep - twopi;
               end
           end
           mp    = mp + pl;
           argpp = xls - mp - cosip * nodep;
       end
   end % // if init == 'n'

   global idebug dbgfile
   if idebug
       debug1;
   end

   return;
